If there are a foreign substance or a defect (short-out or breaking of wire, etc.) on a semiconductor wafer in the semiconductor manufacturing process, the foreign substance or the defect may cause insulation failure or short circuit of a wiring or a capacitor, or the film failure of a gate oxide film, which may result in the failure of the semiconductor device.
In order to improve the yield of the semiconductor device, it is important to rapidly detect a foreign substance or a defect on the semiconductor wafer in a manufacturing process. A SEM (Scanning Electron Microscope) inspection technique or an optical inspection technique have been publicly known as a technique for detecting a foreign substance or a defect on the semiconductor wafer. The optical inspection technique includes a bright field inspection technique and a dark field inspection technique. In the bright field inspection technique, light is irradiated through an objective lens on the wafer and the reflected and diffracted light are collected through the objective lens. The collected light is photoelectrically converted by the detector so that a defect of the wafer is detected in signal processing. On the other hand, in the dark field inspection technique, light is irradiated on the wafer outside of the NA (Numerical Aperture) of an objective lens and the scattered light is collected by the objective lens. Similarly to the bright field inspection technique, the collected light is subjected to signal processing to detect a defect.
As an optical dark field inspection technique, a method is disclosed (in Patent document 1) in which a highly sensitive and highly reliable foreign substance inspection without false report by a pattern is realized by irradiating a laser on the wafer to detect the scattered light from the foreign substance and comparing the scattered light from the foreign substance with the inspection result of the same type wafer which has been inspected immediately before.
Further, as a technique for inspecting the foreign substance, a method is disclosed (in Patent documents 2 to 4) in which coherent light is irradiated on the wafer and light generated by the repeated patterns on the wafer is eliminated by the space filter to emphasize and detect a foreign substance and a defect which are not repeated.